There are many subterranean reservoirs which contain petroleum the viscosity of which is so great that relatively minor amounts thereof can be recovered from a formation by so called primary recovery. Many processes have been described in the prior art for increasing the recovery of viscous petroleum from these formations, and a few have been successfully applied on a commercial basis. Steam flooding is the most successful method utilized commercially for this purpose, and there are numerous commercial steam flood operations on-going at the present time. While steam flooding has been effective for recovering a significant amount of otherwise unrecoverable viscous petroleum from subterranean formations, it is not entirely satisfactory, especially in certain situations. In a conventional steam drive process, a number of injection wells and a number of spaced apart production wells are drilled into the formation, and steam is injected into the injection wells to displace petroleum essentially laterally through the formation toward the production wells. The steam that is injected into the formation is usually a two phase mixture, comprising a vapor phase and a liquid phase. Because of the significant difference in the specific gravity or density of these two phases, the vapor phase portion of the steam migrates fairly quickly to the upper portion of the subterranean petroleum containing formation, and essentially all of the hot liquid phase portion of the steam migrates into the bottom portion of the formation. Vapor phase steam is more effective than hot water at displacing viscous petroleum, and so the portion of the formation swept by the steam vapor is desaturated to a greater extent than the portion of the formation swept by the liquid phase steam condensate.
The addition of chemicals to the steam for the purpose of increasing the oil recovery effectiveness of the liquid phase condensate portion of the steam oil recovery fluid has been recognized, and numerous prior art references to be discussed below have disclosed various additives for this purpose. None have proven to be entirely satisfactory, however, and one common problem which reduces the effectiveness of many of the additives which are coinjected with the steam or other oil displacement fluid is the tendency for the formation mineral matrix to absorb the added chemicals, thereafter rendering them ineffective for the purpose of increasing the oil displacement efficiency of the liquid phase portion of the steam. Because of the relatively large amount of petroleum remaining in the formation after termination of a steam drive oil recovery process, there is a significant unfulfilled need for a process to be applied to a formation after conclusion of a steam drive oil recovery process to recover an additional increment of oil remaining after conclusion of the steam flood.